1. Field of the Invention
The present invention relates to a heavy-duty bearing material which is increasingly required with a recent increase in the power of an internal combustion engine.
2. Description of the Related Art
A conventional copper-lead bearing alloy material generally used for an internal combustion engine consists of a Cu-Pb system or Cu-Sn-Pb system alloy. This alloy has an overlay (surface layer) provided on the surface thereof and consisting of a Pb-Sn alloy, a Pb-Sn-Cu alloy, a Pb-Sn-In alloy or the like. Particularly, such a copper-lead bearing alloy material often has an intermediate layer (barrier layer) consisting of nickel or the like and interposed between the alloy and the overlay in order to prevent the diffusion of tin or indium contained in the overlay into the alloy.
A sliding member has a sintered copper alloy layer to which 1 to 20% by weight of Ni-B compound is added for improving the wear resistance of a cylindrical bush without an overlay, as disclosed in Japanese Patent Application of Serial No. 2-333283 which had not been published at the filing time of the parallel patent application in Japan corresponding to the present application.
In order to prevent the diffusion of tin, indium or the like into the copper-lead bearing alloy, which is contained in an overlay provided on the surface of a copper-lead bearing alloy, a barrier nickel layer (anti-diffusion layer) is generally interposed between the copper-lead bearing alloy and the overlay. However, when the barrier nickel layer is present, there is a problem that if the overlay is worn out during slide-contacting with a shaft of mating sliding member, the barrier nickel layer having poor anti-seizure property is exposed and causes seizure with the mating sliding member. In addition, the production cost is increased by providing the barrier layer. On the other hand, when the barrier nickel layer is lacking, there is a problem that tin, indium or the like contained in the overlay diffuses into the copper-lead alloy and brings about decreases in strength of the overlay and corrosion resistance property.
A bearing alloy material having excellent fatigue resistance, wear resistance and higher strength than that of conventional Cu-Sn-Pb system alloy materials is increasingly demanded with recent increases in the power and performance of engines.
In order to improve the strength and fatigue resistance of a lead-bronze alloy which is known as an engine bearing material, tin content may be increased while decreasing lead content. However, although this expedient prevents diffusion of tin contained in the overlay into the lead-bronze alloy, it causes problems that the heat conductivity of the lead-bronze alloy is significantly deteriorated by an increase in the tin content, and that the anti-seizure property and embeddability of foreign substances (hereinafter referred to as "embeddability") are deteriorated by a decrease in the lead content.